Fault_Simulation_and_ATPG_Expanded_Presentation (1).pptx

Fault_Simulation_and_ATPG_Expanded_Presentation (1).pptx

1. Fault Simulation and ATPG Comprehensive and Detailed Overview

2. Introduction to Digital Testing Digital testing ensures the functionality and reliability of integrated circuits (ICs). It identifies manufacturing defects and validates design correctness. Common testing techniques include simulation, emulation, and hardware testing. Fault simulation and ATPG are core techniques for production testing.

3. Overview of Fault Simulation Fault simulation verifies how a circuit responds in the presence of faults. It determines the effectiveness of test patterns for detecting modeled faults. Used extensively during post-layout verification and production test planning.

4. Types of Fault Models Stuck-at Faults: Signal permanently stuck at logic 0 or 1. Bridging Faults: Two signals shorted causing unintended logic interaction. Open Faults: Disconnected nets or pins. Delay Faults: Caused by timing violations or degraded paths.

5. Stuck-at Fault Model Most widely used and well-supported by ATPG tools. Assumes a wire is stuck permanently at 0 or 1 regardless of logic. Simple yet effective model for many manufacturing defects. Basis for classical ATPG algorithms like D-Algorithm and PODEM.

6. Delay Fault Models 1. Transition Fault: Assumes slow-to-rise or slow-to-fall transitions. 2. Path Delay Fault: Targets specific long paths with potential delay violations. Important for deep sub-micron technologies with tight timing margins.

7. Fault Simulation Techniques Serial: Simulates one fault at a time; accurate but slow. Parallel: Simulates multiple faults in a single pass using parallelism. Deductive: Symbolic simulation using fault lists. Concurrent: Uses data structures to simulate multiple faults efficiently.

8. Pros and Cons of Simulation Methods Serial: + High accuracy - Low performance Parallel: + Fast - High memory usage Deductive: + Handles many faults - Complex to implement Concurrent: + Good trade-off - May be limited by circuit size

9. Fault Simulation Workflow 1. Load fault list from fault model. 2. Apply input test patterns. 3. Inject faults and simulate output. 4. Compare faulty and fault-free outputs. 5. Calculate fault coverage and undetected faults.

10. What is ATPG? ATPG (Automatic Test Pattern Generation) creates input vectors to detect specific faults. Optimizes for maximum fault coverage with minimum number of patterns. Targets faults defined by models such as stuck-at or delay. Central to Design-for-Test (DFT) methodologies.

11. ATPG Workflow 1. Identify target faults from netlist. 2. Select a fault and determine controllability and observability. 3. Use ATPG algorithms to generate a pattern. 4. Simulate the pattern to ensure fault detection. 5. Repeat for all faults, then optimize patterns.

12. Classical ATPG Algorithms D-Algorithm: Propagates a fault signal using D and D’ logic. PODEM: Backtracks through logic to justify fault activation and propagation. FAN: Fanout-oriented ATPG with efficient heuristics. Each algorithm has trade-offs in speed, complexity, and fault coverage.

13. PODEM in Detail 1. Select objective based on fault location. 2. Justify objective using backtracing. 3. Simulate to check if fault is propagated to output. 4. If not, backtrack and try alternate values. Efficient for large circuits due to guided search.

14. Test Pattern Compression X-Filling: Fills don’t care bits to increase detection. Static and dynamic compaction reduce pattern count. Helps reduce test time and tester memory. Crucial for handling large-scale SoC designs.

15. Fault Coverage Metrics Fault Coverage = (Detected Faults / Total Faults) * 100% High fault coverage implies better test quality. Often targets >95% for production. Coverage analysis guides additional test generation.

16. DFT and Scan Insertion DFT inserts structures to simplify testing. Scan Design chains flip-flops for shift-in and shift-out testing. Scan enables ATPG to access internal states efficiently. Essential for achieving high fault coverage.

17. Built-In Self-Test (BIST) BIST embeds test generation and evaluation logic inside the chip. Uses Linear Feedback Shift Registers (LFSRs) and signature analyzers. Supports at-speed testing and self-diagnosis. Common in memory and analog/mixed-signal BIST.

18. ATPG Tools Commercial: Synopsys TetraMAX, Cadence Modus, Mentor FastScan. Open-source: ATALANTA, GOS, GATE. Tools integrate with EDA flows for seamless test generation. Choice depends on circuit complexity, support, and budget.

19. Challenges in ATPG and Simulation 1. Large design sizes increase computational effort. 2. Timing-aware ATPG is complex and resource-heavy. 3. Managing power and IR-drop during testing. 4. Multi-clock and asynchronous designs pose test access issues.

20. Trends and Innovations 1. Machine Learning aids test generation and fault prediction. 2. High-Level ATPG at RTL for early testing. 3. Hybrid approaches mix simulation and formal techniques. 4. ATPG for Security: Trojans and side-channel attack detection.

21. Conclusion and Future Outlook Fault Simulation and ATPG remain critical in chip manufacturing. Ongoing advances in AI, formal methods, and automation improve capabilities. Key to producing reliable, efficient, and testable integrated circuits. Future includes adaptive and self-healing testing systems.